455 H.O. Oil Temp Issue
I have a '71 Trans Am with the 455 H.O. that I'm planning on rebuilding this winter. Ever since I got it some 30 years ago, the oil temperature has been very hot, sometimes reaching 300 degrees. I installed an oil cooler that kept it in the 200 to 250 degree range, and both prior rebuilds were done to factory clearances.
The water temps never got over 200 degrees with the AC on. If I ran without a thermostat, as it came from the used car lot, it was 140-160 degrees. Obviously, the oil wasn't transferring its heat to the water.
When I got this Pontiac, it was used and abused, and the engine was already rebuilt. When I took it apart, the connecting rods were damaged and in the wrong spots. During its second rebuild, I added the SD rods and oil pump, but the problem continued.
So when I tear it down again, what should I look for and how can I fix this?
John McGibney
Ronkonkoma, NY
Jim Taylor responds:
It's not uncommon for '71 and '72 455 H.O.s to run high engine-coolant and oil temperatures. We've found big-inch low-compression engines with today's pump gas can run EGTs of nearly 1,500 degrees. This is obviously too high. The ideal temperature would be about 1,350 degrees.
If your fan has been changed, find a GM piece along with an HD fan clutch to get the desired amount of cfm moving across the cast iron to take heat away. Also, make sure the engine is not running too lean. A lean carb condition could cause very high upper-cylinder temps, which super-heats the area of the head where the valvesprings sit.
The hottest part of an engine is at the exhaust crossover area. In the center of the head there are two exhaust valves next to each other. Each pushrod delivers about three gallons of oil per hour to the rocker arms and springs. This is where oil can pick up extra heat.
I suggest filling the heads with molten aluminum at the head's common heat-riser areas. This separates the two exhaust valves at the No. 4 and No. 6, as well as the No. 3 and No. 5 cylinders, and doesn't let their exhaust come up through the head on its way to the intake crossover. The fan and aluminum fill in the heat-riser area are two things you could do at the time of the rebuild.
You may think, like many people do, that oil temperature and engine-coolant temperature should be the same. They never are. Oil is usually 50 degrees hotter than water temps. So if the water temp is 200 degrees, your oil temps will probably be around 250 degrees. This is normal.
The technicians at Valvoline tell us that 250-270 degrees is ideal for the VR-1 30W oil we use here. If the temperature reaches 300 degrees, we use SYN Power full synthetic.
Oil that is squeezed and pushed through a lubrication system is heated by
hydraulic pressure. Pressure causes heat, which is natural in a system of 30 to 40W oil at 50-60 psi.
It's good to know your engine oil temp so you can use oil that won't break down. Thanks for the question.
Mystery "Sp" Cast In The Block
I have a two-bolt, 400ci short-block from a black '69 Catalina four-door that has a large "SP" cast into the side of it, just ahead of the front freeze plug. The engine code is YD and it has an engine serial number directly above it. Its block casting is No. 9790071.
Have you ever seen another Pontiac block with "SP" cast into the side, and do you know what it stands for?
Jim Skelton
Cleveland, WI
Rocky Rotella responds:
According to my references, YD is the correct engine code for the 400ci two-barrel used in select '69 B-body applications, and it sounds like yours was in its original application when you purchased it.